In vivo CRISPR screening identifies metastasis suppressors in triple-negative breast cancer

Metastatic cancer remains the leading cause of cancer-related mortality, yet tumor cell-intrinsic mechanisms restraining metastatic dissemination remain incompletely defined. Here, we perform an unbiased in vivo genome-wide CRISPR/Cas9 loss-of-function screen in a breast cancer xenograft model to identify regulators of metastatic progression. This approach uncovers clinically relevant metastasis suppressor genes (MSGs), including VPS45, CMTR2, RBSN, and NF2, whose loss enhances lung colonization. Functional validation demonstrates that depletion of these genes promotes epithelial-to-mesenchymal transition, migration, invasion, intravasation, and angiogenesis, whereas CRISPR-mediated activation suppresses metastatic spread. Integration with patient datasets reveals reduced expression in tumors and associations with advanced disease, with higher expression trending toward improved outcomes. Notably, CMTR2 loss induces vascular remodeling and intratumoral heterogeneity, supporting a role in tumor-vascular interactions. Collectively, this study identifies a network of MSGs that constrain tumor dissemination and highlights the power of in vivo CRISPR functional genomics to uncover regulators of metastatic disease.